The present invention relates generally to a subsea wellhead assembly interface, and more particularly to a high pressure seal that is formed between the tubing spool and a casing hanger connected to the wellhead.
In conventional subsea wellhead assemblies, a tubing spool connects the wellhead to the blowout preventor stack (“BOP”). As used herein, the terms “connect,” “connects,” and “connected,” are intended to mean either indirect or direction connection. Thus, if a first device “connects” to a second device, that connection may be through a direct connection or through an indirect connection via other devices or connectors. A gasket is in turn seated between the wellhead and the tubing spool to prevent the loss of pressure out of the system. The gaskets used in such systems are typically formed of solid metal rings and are designed to seal at 15,000 psi (15 ksi). For production pressures of 20 ksi, higher rated gaskets need to be used. Furthermore, an 18¾ inch (15 ksi) BOP is required to be used during drilling with wellhead assemblies that will experience production pressures of 20 ksi during production.
It has been desired to construct wellhead assemblies that can withstand 20 ksi production pressures without the need for BOPs as large as 18¾ inches. It is more commercially viable to develop a 13⅝ inch (20 ksi) BOP than a 18¾ inch (20 ksi) BOP. The present invention achieves the desired balance between being able to form a pressure seal that can withstand production pressures of 20 ksi and which can do so within a wellhead assembly that employs a 18¾ inch BOP during 15 ksi drilling and a 13⅝ inch BOP during 20 ksi production.